1. Home
  2. Electronics Design
  3. Triac and inductive load

Triac and inductive load

I've always used a hefty SC141 triac in projects and mainly have switched incandescent lamps with it.

I use a triac driver optoisolator followed by the triac, of course, and switch the load.

I know problems can arise with inductive loads.....rf noise? damage to the triac itself?.....but I haven't had any problem controlling an AC outlet with say, a small AC adapter type transformer attached. Small currents....200 - 500 ma or so.

(At least, not so far).

If I wanted to do it right, could I simply use a zero crossing triac driver to eliminate (or considerably) reduce the inductive problem? I've used these before and it's amazing how much RF noise they eliminate.

Isn't it the "kickback" problem with an inductive load? If you're switching on/off at zero crossing, would you get rid of that?

I know also, that there are built in "snubbing" circuits on some of these triacs and also they have very high peak voltage capabilities (2500v or so).

Please enlighten.

THANKS.

Reply to
mkrnews
Loading thread data ...

One of the problems with driving inductive loads is that the current and voltage don't cross zero at the same time, which can confuse the triac's switching.

AFAIK there are at least two solutions to this:

  1. Use a snubber or zero crossing driver.

  1. Switch to alternistors.

The first is well documented for both cases, and you've already found one solution therein ;-)

The second is what I do. An alternistor acts like a triac, but internally it's designed differently so that it can deal with inductive loads.

Reply to
DJ Delorie

You may want to employ a un-inductive load on the circuit like a resistor or use a RC snubber calculated to create minimum phase current for the minimum time. This will keep inductive collapse down to a minimum and maintain load on the circuit to insure the triac stays latched during the holding level of the phase angle.

formatting link
"

Reply to
Jamie

** Are you only switching the load on or off or doing something else ?
** Depends on your the answer to the above.
** What problem ??

Depends on your the answer to the above.

** Zero load switching is not advisable with transformer and many other inductive loads.

Plus zero *voltage* switching devices only "zero switch" loads on - cos as with any triac circuit, the load goes of when the triggering is stopped AND the load current drops below the holding value.

...... Phil

Reply to
Phil Allison

no, it's the voltage step, triacs switch off when the current goes to zero.

If you're switching these devices (on or off, not trying to dim them), properly snubbed triacs should be no worse than mechanical switches

Reply to
Jasen Betts

Alternistors is a new one on me....I'll have to research that today.

Thanks for the help.

Reply to
mkr5000

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.